Rotary type carburetor for stratefied scavenging engine

ABSTRACT

An improved rotary type carburetor for a stratified scavenging engine designed to enable the easy adjustment of air and fuel flow at the time of initial configuration is disclosed. The improved rotary carburetor includes an air intake passage and an air-fuel mixture passage formed in a horizontal direction on a carburetor main body. The throttle valve of the improved rotary carburetor can be fitted into a cylindrical-throttle-valve hole formed orthogonal to a fuel and an air passage of the carburetor main body. The throttle valve has the air supply side valve hole formed on the air intake passage side and a fuel supply side valve hole formed on the air-fuel mixture passage side.

CROSS REFERENCED TO RELATED APPLICATION

The subject application is a continuation of U.S. Appl. No. 17/134,910,filed Dec. 28, 2020, which claims the benefit of Japanese PatentApplication No. 2020-001166, filed Jan. 8, 2020, both of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The disclosure relates generally to a rotary type carburetor for astratified scavenging engine suitable for a two-stroke internalcombustion engine such as a power saw or a lawn mower.

BACKGROUND

The use of conventional rotary throttle valve carburetors found intwo-stroke internal combustion engines has greatly increased as they areessential in portable machinery for agriculture, forestry, and smallvehicle. The rotary throttle valve is formed from a rotor that rotatesin the axial direction of the valve.

One type of rotary type carburetor, as disclosed in JP H10-252565A,employs a cylindrical throttle valve, which has a throttle-valve holeand a metering pin orthogonal to an air intake passage of the carburetormain body. The throttle valve is capable of rotating and moving in theaxial direction at the time of rotation. By rotating the throttle valve,the amount of air flow is controlled while changing the degree ofoverlapping with the air intake passage of the throttle valve hole. Inaddition, the fuel flow is controlled by changing the insertion depth ofthe metering pin into the fuel nozzle.

The throttle valve has two circular shape valve holes in a mutual axisrotor. In order to open a fuel supply side valve hole first when idling,the rotor outer diameter of the air supply side valve hole is enlarged.The rotor is configured in two stages. For example, FIG. 1 shows athrottle valve 6 that includes a semicircular air supply side valve hole7 that is oriented upward (toward rotation shaft 11) from a partitionwall 9. Throttle valve 6 also includes a lower semicircular fuel supplyside valve hole 8.

FIG. 2 shows a carburetor main body 1 having an air intake passage 2, afuel-air mixture passage 3, and wall 4. The throttle valve opposing thesemicircular air supply side valve hole 7 and the lower semicircularfuel supply side valve hole 8. This has the benefits of having a simpleconstruction, the carburetor can be miniaturized because the height ofthe carburetor can be minimized, and it is also possible to design asmall engine.

However, as illustrated in FIG. 1 and FIG. 2 , a conventional throttlevalve, with a partition wall 9 and valve holes, has difficultymaintaining an idle air-fuel ratio with a small amount of air. Thisissue occurs because throttle valve 6 is displaced downwards during idleopening and the air supply side valve hole 7 opens first. Additionally,the fuel supply side valve hole 8 is constructed to open afterwards.

FIG. 3 shows a conventional throttle valve 6 having a groove pocket 10.By forming the groove pocket 10 on the opening edge of the upstream end,which faces the accelerating rotation direction side of the fuel supplyside valve hole 8, driving becomes possible between the initial stagesof idling to intermediate idle opening in the groove pocket 10 of thefuel supply side valve hole 8. Because all of the air and fuel issupplied to the engine side via the groove pocket 10, the emulsionbecomes relatively high speed, which for a rotary type carburetorimproves rotation drop-in during the idle full body position change bysupplying the emulsion to the engine as disclosed in JP 2008-163754A.

Generally, it is necessary to correct dispersion when assembling and itis necessary to initialize to conform with exhaust gas regulations. Abench test and an initialization must be performed so that the air flowand fuel flow are suitable at least in an idle region. In addition tocontrolling the air flow while changing the overlap between the throttlevalve hole of the throttle valve and the air intake passage formed onthe carburetor main body, the fuel flow is controlled by changing theinsertion depth of the metering pin into the fuel nozzle. The initialconfiguration moves the throttle valve in the axial direction using anidle adjusting screw in the idling region where the groove pocketoverlaps the air-fuel mixture passage (not shown). The air flow and thefuel flow are adjusted to a predetermined target specification (see FIG.4 ) by adjusting the insertion depth into the fuel nozzle, which isadjusted by moving the metering pin in the axial direction using a fueladjusting screw (not shown).

Increases or decreases in the fuel flow can be achieved by moving thethrottle valve in the axial direction. When the fuel is increased usingan adjusting screw (not shown) in the idling region illustrated in FIG.5A, the throttle valve 6 moves in the axial direction (shown in theupward direction) such that groove pocket 10 of the fuel supply sidevalve hole 8 moves in between the air-fuel mixture passage 3 of thecarburetor main body 1 as illustrated in FIG. 5B.

In this conventional example, the degree of opening of the groove pocket10 of the fuel supply side valve hole 8 in the throttle valve 6necessarily increases (the diagonal line portion illustrated) becausethe air-fuel mixture passage 3 is a downwardly oriented semicircularshape, and the air flow (air) is simultaneously changed simply bychanging the fuel flow (fuel).

Thus, even if the fuel flow is adjusted to a state where the prescribedair flow is determined to first reach the target specification, the airflow will change. This makes the adjustment of the initial configurationto a predetermined target specification as illustrated in FIG. 4extremely difficult. In this scenario, productivity is extremelyunfavorable because adjustments need to be made by carrying out manyfine adjustments of the air and fuel flow in the vicinity of the targetspecification as illustrated in FIG. 6 or FIG. 7 .

Furthermore, Japanese Application No. JP 2002-256975A discloses a rotarycarburetor that simplifies idling adjustments by having adjusting screwsthat can each individually adjust the air flow and fuel flow. However,as described above, the difficulty in adjusting the initialconfiguration originates in the shape of the groove pocket 10 of thefuel supply side valve hole 8 and in the downwardly orientedsemicircular shape of the air-fuel mixture passage 3 formed on thecarburetor main body 1. Because the air flow changes simultaneously whenadjusting the fuel flow, by moving the throttle valve in the axialdirection, it fails to resolve the complications in the adjustment ofthe initial configuration.

SUMMARY OF INVENTION

One of the objectives of the present disclosure is to obtain improvementin engine efficiency and productivity by making it easy to adjust theair flow and the fuel flow at the time of initial configuration of theidle driving region to achieve a predetermined target specification.

Disclosed herein is an improved rotary type carburetor (improved rotarycarburetor) for a stratified scavenging engine designed to enable theeasy adjustment of air and fuel flow at the time of initialconfiguration. The improved rotary carburetor includes an air intakepassage and an air-fuel mixture passage formed in a horizontal directionon a carburetor main body. The throttle valve of the improved rotarycarburetor can be fitted into a bottomed-cylindrical-throttle-valve holeformed orthogonal and perpendicular to each passage of the carburetormain body. The throttle valve has an air supply side valve hole formedon the air intake passage side and a fuel supply side valve hole formedon the air-fuel mixture passage side.

The improved rotary carburetor includes a groove pocket formed on anopening edge on an upstream end, which is on an accelerating rotationdirection side of the fuel supply side valve hole (of the throttlevalve). The improved rotary carburetor also includes an opening shape onthe downstream side of an opening end on at least the throttle valveside of the air-fuel mixture passage, which is formed on a perpendicularside parallel to an axis of the throttle valve.

In some embodiments, the cross-sectional shape of the air-intake passageformed on the carburetor main body can be an upper semicircle. Thecross-sectional shape of the air-fuel mixture passage can be a lowersemicircle. The upper and lower semicircles are separated by a partitionwall. The cross-sectional shape of the air-supply-side valve hole can bethe upper semicircle, and a cross-sectional shape of thefuel-supply-side valve hole side can be the lower semicircle. Similarly,the air-supply-side and the fuel-supply-side valves can form a circleseparated by a partitioned wall. In this way, the carburetor main bodycan be miniaturized.

Additionally, the improved rotary carburetor includes a groove pocketformed on the opening edge on the upstream end, which is on theaccelerating rotation direction side of the fuel supply side valve. Thefuel supply side valve can have a tongue-shaped opening end havingparallel opposing sides. In this way, the improved rotary carburetor canmake adjustments easily and accurately.

Furthermore, the shape (e.g., length, height, width) of the openingshape of the opening end of the throttle valve side is selected suchthat a portion formed by the parallel opposing sides of the groovepocket does not extend further into the air-fuel mixture passage duringan adjustment of the throttle valve. In some embodiments, the openingshape of the opening end of throttle valve side of the air-fuel mixturepassage formed on the carburetor main body is rectangularly shaped.

The improved rotary carburetor can improve efficiency and productivityby adjusting the air flow and fuel flow to a predetermined targetspecification (spec) by adjusting the insertion depth into the fuelnozzle by establishing the air flow because the opening area into theair-fuel mixture passage of the groove pocket does not change or onlychanges slightly even when the fuel is increased or decreased by movingthe throttle valve in an axial direction using an adjusting screw in theidle region wherein the groove pocket overlaps the air-fuel mixturepassage.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description, isbetter understood when read in conjunction with the accompanyingdrawings. The accompanying drawings, which are incorporated herein andform part of the specification, illustrate a plurality of embodimentsand, together with the description, further serve to explain theprinciples involved and to enable a person skilled in the relevantart(s) to make and use the disclosed technologies.

FIG. 1 is a perspective diagram of a conventional throttle valve.

FIG. 2 is a front view of a conventional carburetor main body.

FIG. 3 is a perspective diagram of another conventional throttle.

FIG. 4 is a state diagram illustrating a state of adjusting to thetarget specification by adjusting the fuel flow and air flow in the idleregion at the time of delivery.

FIGS. 5A and 5B illustrate a conventional throttle valve exposed to anair-fuel mixture passage of a carburetor main body in a conventionalidle region in different states.

FIG. 6 is a state diagram illustrating a state of adjusting to thetarget specification by adjusting the fuel flow and air flow in the idleregion at a time of delivery.

FIG. 7 is a state diagram illustrating a state of adjusting to thetarget specification by adjusting the fuel flow and air flow in the idleregion at a time of delivery.

FIG. 8 is a front view of a carburetor main body in accordance with someembodiments of the present disclosure.

FIG. 9 is a side view with a portion broken down along the Y-Y line ofFIG. 1 in accordance with some embodiments of the present disclosure.

FIG. 10 is a perspective diagram of a throttle valve in accordance withsome embodiments of the present disclosure.

FIG. 11A illustrates a throttle valve in a state prior to adjustment ofthe fuel flow in accordance with some embodiments of the presentdisclosure.

FIG. 11B illustrates the throttle valve shown in FIG. 11A in a statefollowing adjustment of the fuel flow in accordance with someembodiments of the present disclosure.

FIG. 12 is a front view of a carburetor main body in accordance withsome embodiments of the present disclosure.

FIG. 13A illustrates a throttle valve in a state prior to adjustment ofthe fuel flow in accordance with some embodiments of the presentdisclosure.

FIG. 13B illustrates the throttle valve shown in FIG. 13A in a statefollowing adjustment of the fuel flow in accordance with someembodiments of the present disclosure.

The figures and the following description describe certain embodimentsby way of illustration only. One skilled in the art will readilyrecognize from the following description that alternative embodiments ofthe structures and methods illustrated herein may be employed withoutdeparting from the principles described herein. Reference will now bemade in detail to several embodiments, examples of which are illustratedin the accompanying figures. It is noted that wherever practicablesimilar or like reference numbers may be used in the figures to indicatesimilar or like functionality.

DETAILED DESCRIPTION Improved Rotary Carburetor

FIG. 8 illustrates a front view of a rotary type carburetor 800 for astratified scavenging in accordance with some embodiments of the presentdisclosure. Carburetor 800 includes a carburetor main body 1, an airintake passage 2 formed through carburetor main body 1, an air-fuelmixture passage 3 formed through the carburetor main body 1, and apartition wall 4 formed on the carburetor main body 1 to separate airintake passage 2 and air-fuel mixture passage 3.

FIG. 9 illustrates a cross-section of a portion of rotary carburetor800. FIGS. 8 and 9 will be discussed concurrently. Rotary carburetor 800includes an air intake passage 2 and an air-fuel mixture passage 3, bothpassages 2,3 can have a semicircular cross-sectional shape. Passages 2and 3 are separated by partition wall 4. In the configuration shown inFIG. 8 , air intake passage 2 can be located in the upper region (on topof partition wall 4) and air-fuel mixture passage 3 can be located inthe lower region (below the partition wall 4). In some embodiments,passages 2 and 3 are formed from a common circular/cylindrical holeseparated by partition wall 4.

Referring to FIG. 9 , the left end of both air-fuel mixture passage 3and air intake passage 2 are connected to an air cleaner on the upstreamside. The right end of both air-fuel mixture passage 3 and the airintake passage 2 are connected to an air intake passage and a scavengeair passage via an engine side insulator on the downstream side (notillustrated in drawings).

In some embodiments, throttle valve 900 is disposed in a bottomed,cylindrical throttle valve hole 5 formed perpendicular to carburetormain body 1. Throttle valve 900 is configured to be rotated by arotation shaft provided on an axis and to move in the axial directionalong with this rotation. In some embodiments, throttle valve 900 isconfigured to move in the axial direction of the rotation shaft while itis rotating by the rotation shaft (not shown).

FIG. 10 illustrates throttle valve 900 in accordance with someembodiments of the present disclosure. Throttle valve 900 can be asingle cylinder having substantially the same diameter as the throttlevalve hole 5 illustrated in FIGS. 8 and 9 . In some embodiments, airsupply side valve hole 7 and a fuel supply side valve hole 8 are formedin the throttle valve 900 penetrating across the radial direction ofthrottle valve 900. The air supply side valve hole 7 can have an uppersemicircular cross-sectional shape.

Fuel supply side valve hole 8 can also have a lower semicircularcross-sectional shape. A partition wall 9 is disposed between air supplyside valve hole 7 and fuel supply side valve hole 8. In someembodiments, holes 7, 8 can be formed from a common cylindrical/circularhole that is mutually separated.

Air supply side valve hole 7 is configured to supply air to air intakepassage 2 to control the flow ratio of scavenging air. Fuel supply sidevalve hole 8 is configured to supply a fuel-air mixture to air-fuelmixture passage 3 to control engine output. In some embodiments, airintake passage 2, air-fuel mixture passage 3, air supply side valve hole7, and the fuel supply side valve hole 8 can have substantially the samecross-sectional shape. Additionally, both passages 2 and 3 can be formedfrom one common cylindrical hole such that they mutually coincidethrough partition walls 4 and 9.

Groove pocket 10 can be formed on the fuel supply side valve hole 8 ofthrottle valve 900. Groove pocket 10 can be formed on the opening edgeof fuel supply side valve hole 8. The opening edge can be on theupstream end of the throttle valve 900, which is on the acceleratingrotation direction side.

When throttle valve 900 is idle, air-fuel mixture passage 3 is openedwhile air intake passage 2 is closed due to throttle valve 900 beingfirst and due to the partial overlap of groove pocket 10 and theair-fuel mixture passage 3. In other words, because groove pocket 10 offuel supply side valve hole 8 is fluidically communicated first, all airand fuel are supplied to the engine side via the groove pocket 10.Additionally, fuel emulsion supplied to the engine can become relativelyhigh speed, groove pocket 10 can bring about the action and effect ofimproving engine speed reduction in idling and all positions changing.

In some embodiments, groove pocket 10 can have a tongue-shaped openingend with parallel opposing sides 101 and 102 separated by a gaptherebetween. Side 102 can start at opening edge 81 on the upstream endof the accelerating rotation direction of fuel supply side valve hole 8.

Additionally, the opening on the downstream side of opening end 31 (seeFIG. 9 ) on at least the throttle valve 900 side of the air-fuel mixturepassage 3 is formed on a perpendicular side 32 (see FIG. 8 ) parallel tothe axis of the throttle valve 900. The opening on the downstream sideof opening end 31 has a prescribed length and shape such that the extentof the opening (e.g., total surface area exposed) is constant from theinitial configuration and after the adjustment of the throttle valve900. In other words, the total surface area of opening 10 remainsconstant during any adjustment of throttle valve 900.

In this manner, when throttle valve 900 rotates horizontally to the idleoperation position, the groove pocket 10 first overlaps with theair-fuel mixture passage 3, which cause fuel supply side valve hole 8and air-fuel mixture passage 3 to fluidically communicate. Additionally,fuel supply side valve hole 8 is opened before the air supply side valvehole 7.

Throttle valve 900 rotates horizontally around a rotation shaft 11 dueto the rotation of a throttle lever 13 attached to the terminal of therotation shaft 11 protruding from a throttle valve cover 12. Throttlelever 13 and throttle valve 900 rotate horizontally while graduallybeing lifted by, for example, a cam mechanism provided between thecarburetor main body 1 and throttle lever 13. To the extent of theopenings of the air supply side valve hole 7, the fuel supply side valvehole 8, air intake passage 2, and air-fuel mixture passage 3 formed onthe carburetor main body 1 are changed, a prescribed amount of fuel isreleased from a metering chamber 19. Metering chamber 19 is isolatedfrom an air chamber 18, which is open to the atmosphere from a venthole, by a metering diaphragm 17 and positioned on the bottom surface ofthe side opposite the throttle valve cover 12.

Needle 15 can be attached to the rotation shaft 11. Needle 15 canprotrude and extend from inside fuel supply side valve hole 8 across airsupply side valve hole 7 from the upper portion. Fuel flows out from amain nozzle 20 provided in the fuel supply side valve hole 8 (detaileddescription thereof will be omitted).

FIGS. 11A and 11B illustrate rotary type carburetor 800 for a stratifiedscavenging engine in accordance with some embodiments of the presentdisclosure. In an idle position, groove pocket 10 portion (of the fuelsupply side valve hole 8 in the throttle valve 900) overlaps the openingon the downstream side of the air-fuel mixture passage 3 formed oncarburetor main body 1. In the bench test, throttle valve 900 is movedin the axial direction using an adjusting screw (not illustrated in thedrawings), and the air flow and the fuel flow are adjusted to apredetermined target specification by adjusting the insertion depth intothe fuel nozzle. The insertion depth can be adjusted by moving themetering pin in the axial direction using a fuel adjusting screw (notillustrated in the drawings), which can be integrated into the engine.However, because the opening on the downstream side of the opening end31 is formed on the perpendicular side 32 parallel to the axis of thethrottle valve 900 and with a prescribed length, and even if the fuelflow is increased by adjusting the throttle valve 900 to move, forexample, in the direction of the arrow as illustrated in FIG. 11B, theextent of the opening from the groove pocket 10 of the fuel supply sidevalve hole 8 on the throttle valve 900 does not change as it does in theconventional example illustrated in FIGS. 5A and 5B. Therefore, the fuelflow can be adjusted without affecting the air flow in the throttlevalve 900, these can be easily adjusted to a predetermined targetspecification. In this manner, productivity is improved.

In some embodiments, because groove pocket 10 portion of the fuel supplyside valve hole 8 in throttle valve 900 has a tongue-shaped opening end(with parallel opposing sides 101 and 102 disposed having a prescribedgap therebetween), the amount of the opening from the groove pocket 10does not change even if the fuel flow is increased by adjusting thethrottle valve 900. Stated differently, opening does not extend furtherinto air-fuel mixing chamber 3 when throttle valve 900 is adjusted. Inthis way, adjustment can be made on rotary type carburetor 800 simplerand more efficient. Additionally, in the above manner, carburetor 800can be made more efficient when using a groove pocket having differentshape such as the tongue shape illustrated in FIG. 10 . In someembodiments, the size of the opening of groove pocket 10 is reducedstarting from edge 81 of valve hole 8. In other words, valve hole 8 canhave two portions, a larger portion and a smaller portion. Groove pocket10 is the smaller portion and can be disposed on the downstream side.When the fuel flow is increased by adjusting the throttle valve 900 due,the opening (i.e., groove pocket 10) on the downstream side of theopening end 31 is formed on the perpendicular side 32 parallel to theaxis of the throttle valve 900 having a prescribed length.

FIGS. 12 and 13 illustrate a carburetor 1200 in accordance with someembodiments of the present disclosure. Carburetor 1200 can have one ormore of the features of carburetor 800 as described in FIGS. 8-11 .While the opening on the downstream side of the opening end 31 on thethrottle valve 900 side forms a perpendicular side 32 parallel to theaxis of the throttle valve 900 having a prescribed length on thedownwardly oriented semicircular air-fuel mixture passage 3 formed onthe carburetor main body 1 in the embodiments illustrated in FIG. 1 toFIG. 4 , these differ in that the shape of the air-fuel mixture passage3 is formed in a rectangular shape including the perpendicular side 32.

The action and effect of carburetor 1200 are the same as the embodimentsillustrated in FIGS. 8 to 11 . However, while the opening on thedownstream side of the opening end 31 (see FIG. 2 ) on the throttlevalve 900 side is formed on a perpendicular side 32 parallel to the axisof the throttle valve 900 having a prescribed length, wherein theair-fuel mixture passage 3 in the embodiments illustrated in FIG. 1 toFIG. 4 is basically in a downwardly oriented semicircular shape, theprocessing of the air-fuel mixture passage 3 is simplified.

Although certain features from a conventional carburetor (FIG. 1 ) andfeatures from the improved carburetor (FIG. 8 ) of the presentdisclosure may have the same reference numbers, those features with thesame reference number may not be the same. Where the reference numbersare the same in both the conventional carburetor and the new & improvedcarburetor, they are for reciting the name of the components. Forexample, passage 7 of throttle valve 900 can be completely differentfrom passage 7 of throttle valve 6. In another example, groove pocket 10of throttle valve 900 (FIG. 10 ) can be different from groove pocket 10throttle valve 6 of FIG. 3 . Additionally, items in FIGS. 8 through 13Bwith the same reference numbers as items in FIG. 1-5B can have one ormore of the same features and functionalities as described in FIGS. 1through 5B. For example, passage 7 of throttle valve 900 (FIG. 9 ) canhave one or more of the same features/functions of passage 7 of throttlevalve 6 in FIG. 1 .

Reference in the specification to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the invention. The appearances of the phrase “in one embodiment” invarious places in the specification are not necessarily all referring tothe same embodiment.

The figures and the following description describe certain embodimentsby way of illustration only. One skilled in the art will readilyrecognize from the following description that alternative embodiments ofthe structures and methods illustrated herein may be employed withoutdeparting from the principles described herein. It is noted thatwherever practicable similar or like reference numbers may be used inthe figures to indicate similar or like functionality.

The foregoing description of the embodiments of the present inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the present invention tothe precise form disclosed. Many modifications and variations arepossible in light of the above teaching. It is intended that the scopeof the present invention be limited not by this detailed description,but rather by the claims of this application. As will be understood bythose familiar with the art, the present invention may be embodied inother specific forms without departing from the spirit or essentialcharacteristics thereof. Likewise, the particular naming and division ofthe modules, routines, features, attributes, methodologies and otheraspects are not mandatory or significant, and the mechanisms thatimplement the present invention or its features may have differentnames, divisions and/or formats.

Additionally, the present invention is in no way limited toimplementation in any specific programming language, or for any specificoperating system or environment. Accordingly, the disclosure of thepresent invention is intended to be illustrative, but not limiting, ofthe scope of the present invention, which is set forth in the followingclaims.

Additionally, the present invention is in no way limited toimplementation in any specific programming language, or for any specificoperating system or environment. Accordingly, the disclosure of thepresent invention is intended to be illustrative, but not limiting, ofthe scope of the present invention, which is set forth in the followingclaims.

1. A rotary type carburetor for a stratified scavenging enginecomprising: an air intake passage and an air-fuel mixture passage formedin a horizontal direction on a carburetor main body; and a throttlevalve fitted into a bottomed cylindrical throttle valve hole formedorthogonal and perpendicular to a passage of the carburetor main body,wherein the throttle valve has an air supply side valve hole formed onthe air intake passage side, a fuel supply side valve hole formed on theair-fuel mixture passage side, a groove pocket formed on an opening edgeon an upstream end that is on a side of an accelerating rotationdirection of the fuel supply side valve, and an opening shape on adownstream side of an opening end on at least the throttle valve side ofthe air-fuel mixture passage is formed on a perpendicular side parallelto an axis of the throttle valve.
 2. The rotary type carburetor of claim1, further comprising: a cross-sectional shape of the air intake passageformed on the carburetor main body is an upper semicircle; across-sectional shape of the air-fuel mixture passage is a lowersemicircle, making a circle separated by a partition wall; across-sectional shape of the air supply side valve hole formed on thethrottle valve is an upper semicircle; and a cross-sectional shape ofthe fuel supply side valve hole side is a lower semicircle, making acircle separated by a partition wall.
 3. The rotary type carburetor fora stratified scavenging engine of claim 1, wherein the groove pocketcomprises a tongue-shaped opening end having parallel opposing sides. 4.The rotary type carburetor for a stratified scavenging engine of claim3, wherein the opening shape of the opening end of the throttle valveside has a shaped such that the opening shape has a constant area ofexposure to the air-fuel mixture passage.
 5. A rotary type carburetorcomprising: a cylindrical throttle valve hole formed orthogonal andperpendicular to a passage of the carburetor main body; a throttle valverotationally fitted into the cylindrical throttle valve hole, thethrottle valve comprises: an air supply side valve hole formed on theair intake passage side, a fuel supply side valve hole formed on theair-fuel mixture passage side, a groove pocket formed on an opening edgeon an upstream end of the fuel supply side valve, wherein the upstreamend comprises a side toward a direction of accelerating rotation; and anopening shape on a downstream side disposed on a perpendicular sideparallel to an axis of the throttle valve.
 6. The rotary type carburetorof claim 5, wherein the air intake passage formed on the carburetor mainbody comprises a cross-sectional shape of a first semicircle; whereinthe air-fuel mixture passage formed on the carburetor main bodycomprises a cross-sectional shape of a second semicircle, wherein theair intake passage is above the air-fuel mixture passage, and whereinthe air intake passage and the air-fuel mixture passage are separate bya partition wall; wherein the air supply side valve hole formed on thethrottle valve comprise a cross-sectional shape of a third semicircle;and wherein the fuel supply side valve hole side comprise across-sectional shape of a fourth semicircle, wherein the thirdsemicircle is above the fourth semicircle and is separated by a secondpartition wall.
 7. The rotary type carburetor of claim 5, wherein thegroove pocket comprises a tongue-shaped opening end having parallelopposing sides.
 8. The rotary type carburetor of claim 5, wherein theopening shape of the opening end of the throttle valve side has a lengthsuch that a portion formed by the parallel opposing sides of the groovepocket formed on the opening edge on the upstream end on theaccelerating rotation direction side of the fuel supply side valve holeof the throttle valve does not extend further into the air-fuel mixturepassage.